Since first posting this thread I have had an e mail in from Bryon Miller in Michigan. With his permission I am reproducing it here. It gives more info on the existence of 744 and 745 tractors in N America. Thanks Bryon.
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Hi John

You might remember me we have met at some past show and I have shared some pictures of my collection. I read your note on the Massey Page and I had some questions and comments. I have not been able to get sign on so I thought I might try this way.

As far as I know there are two 744s in Ontario: one is running which was the one we saw at the last Massey show in Milton which is believed to be a test tractor. The other is owned by I think Don Mc Vitte. I have heard this is not running due to sitting too long without running.

The 744 and 745 from Yuma I heard went to North Dakota. But I have not heard who got them and have not seen them show up at a show. A gentleman in Ohio who's name escapes me but he likes to be called Mr Perkins was putting together a 745 out of parts but I do not think he has finish it.

I have two 744s , one 745 and one 745S. See attached pictures. All of mine came from Australia. The 745s just arriving this year. All of mine are running but need work to fix old repairs and band aids.

You mentioned that Massey sent the rear-ends over. When I compare the 744 to a 44 I see that a gear lube dipstick has been added and the oil fill hole has been added to the side of the casing where on a 44 it is part of the gear shift cover. Also on the back of the transmission case there are extra guess across the back where you could bolt something to the back of the rear end giving a flat surface to bolt to and mounting holes.

Do you know when these where added? My guess is when Massey moved the assembly to Scotland but I have no good information on this. When I got my 745 I was going to change the rear axel because it had a flange welded onto to it to accept a stamped wheel. But when I tried to fit the US axel to the bull gear it was not the correct size. The US was just a little too big. So I am thinking that they ended up making all of the parts in Scotland. I ended up grinding off all the weld and fitting some hubs from a 44 standard.